VXLAN and BGP EVPN Configuration Guide for Dell EMC SmartFabric OS10 Release 10.5.2

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VXLAN BGP EVPN routing

This section describes how EVPN implements overlay routing between L2 segments associated with EVIs belonging to the same tenant on a VTEP. IETF draft draft-ietf-bess-evpn-inter-subnet-forwarding-05 describes EVPN inter-subnet forwarding, Integrated Routing and Bridging (IRB), and how to use EVPN with IP routing between L2 tenant domains.

You set up overlay routing by assigning a VRF to each tenant, creating a virtual-network interface, and assigning an IP subnet in the VRF to each virtual-network interface. The VTEP acts as the L3 gateway that routes traffic from one tenant subnet to another in the overlay before encapsulating it in the VXLAN header and transporting it over the underlay fabric. On virtual networks that associate with EVIs, EVPN IRB is enabled only after you create a virtual-network interface.

When you enable IRB for a virtual network/EVI, EVPN operation on each VTEP also advertises the local tenant IP-MAC bindings learned on the EVPN-enabled virtual networks to all other VTEPs. The local tenant IP-MAC bindings are learned from ARP or ICMPv6 protocol operation. They advertise as EVPN Type-2 BGP route updates to other VTEPs, each of whom then imports and installs them as ARP/IPv6 neighbor entries in the dataplane.

To enable efficient traffic forwarding on a VTEP, OS10 supports distributed gateway routing. A distributed gateway allows multiple VTEPs to act as the gateway router for a tenant subnet. The VTEP that is located nearest to a host acts as its gateway router.

To enable L3 gateway/IRB functionality for BGP EVPN, configure a VXLAN overlay network and enable routing on a switch:
  1. Create a non-default VRF instance for overlay routing. For multi-tenancy, create a VRF instance for each tenant.
  2. Configure globally the anycast gateway MAC address used by all VTEPs.
  3. Configure a virtual-network interface for each virtual network, (optional) assign it to the tenant VRF, and configure an IP address. Then enable the interface.
  4. Configure an anycast gateway IP address for each virtual network. OS10 supports distributed gateway routing.
EVPN supports different types of IRB routing for tenants, VMs, and servers, that connect to each VTEP:
  • Centralized routing: For each tenant subnet, one VTEP is designated as the L3 gateway to perform IRB inter-subnet routing. All other VTEPs perform L2 bridging.
  • Distributed routing: For each tenant subnet, all VTEPs perform L3 gateway routing for the tenant VMs and servers connected to a VTEP. In a large multi-tenant network, distributed routing allows for more efficient bandwidth use and traffic forwarding. IRB routing is performed either:
    • Only on an ingress VTEP.
    • On both ingress and egress VTEPs.

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